OK, I understood that JOINT STEREO should be the default setting for the reasons broadly explained.

Unfortunately Apple confused me with the following text for iTunes, but I guess this is just badly written info : Stereo Mode:In Normal mode, your MP3 files contain one track for the right stereo channel and one track for the left. In many cases, the two channels contain related information. In Joint Stereo mode, one channel carries the information that’s identical on both channels, and the other channel carries the unique information. At bit rates of 160 kbps and below, this can improve the sound quality of your converted audio.

Even with iTunes and its encoder JOINT Stereo is better above 160kbps than Normal. True ?What big a difference is there ? Is it worth to re-encode my CDs to get Joint/320 instead of normal/320 ?

This is a product of confused terminology, and has been the source of a lot of grief.

In the lame encoder (and I think this is the correct terminology) joint stereo refers to a combination of some frames that are encoded as separate left and right channels, and some that are encoded as mid and side channels. In the text you quoted, what they refer to as "normal" mode is in fact left/right encoding and what they refer to as "joint" mode is not joint mode at all, but is instead the mid/side encoding that the encoder is allowed to use on a frame-by-frame basis in joint stereo mode whenever it is a better choice than left/right.

@Micha-ASQ: You should think of Joint-Stereo as a "bit-saver" method. Using it allows the encoder to use more bits for audio, for a specific bitrate.

Joint stereo is important below 160Kbps because the less bits available, the more the encoder benefits from having extra bits.

Above 160Kbps is still important, and that's why LAME uses it whenever is possible, because either it can reduce the file size/bitrate (if using VBR), or the quality can be higher for a specific file size/bitrate (CBR).

On the question about reencoding or not, you have two options:

- Don't spend time evaluating the need, and spend it on doing the new rip/encoding.- Spend time evaluating (ABX) some samples to verify if there's a hearable difference and might not require rip/encoding.

Concretely, since you talk about 320 (CBR, I assume), you probably won't find a difference, but some genres and sounds can fail easier than others.Basically, those that require a higher bitrate than usual when encoded in VBR might end requiring more bits than available even at 320kbps if using simple stereo. (Sometimes even using joint stereo is not enough, but we are entering into killer samples territory now).

MONO is the default mode for mono input files. If "-m m" is specified for a stereo input file, the two channels will be averaged into a mono signal.

STEREO

JOINT STEREO is the default mode for stereo files with fixed bitrates of 128 kbps or less. At higher fixed bitrates, the default is stereo. For VBR encoding, jstereo is the default for VBR_q >4, and stereois the default for VBR_q <=4. You can override all of these defaults by specifing the mode on the command line.

jstereo means the encoder can use (on a frame by frame bases) either regular stereo (just encode left and right channels independently) or mid/side stereo. In mid/side stereo, the mid (L+R) and side (L-R)channels are encoded, and more bits are allocated to the mid channel than the side channel. This will effectively increase the bandwidth if the signal does not have too much stereo separation.

Mid/side stereo is basically a trick to increase bandwidth. At 128 kbps, it is clearly worth while. At higher bitrates it is less useful.

For truly mono content, use -m m, which will automatically down sample your input file to mono. This will produce 30% better results over -m j.

Using mid/side stereo inappropriately can result in audible compression artifacts. To much switching between mid/side and regular stereo can also sound bad. To determine when to switch to mid/side stereo, LAME uses a much more sophisticated algorithm than that described in the ISO documentation.

FORCED MID/SIDE STEREO forces all frames to be encoded mid/side stereo. It should only be used if you are sure every frame of the input file has very little stereo seperation. DUAL CHANNELS Not supported.INTENSITY STEREO

NOW THIS IS INTERESTING: WHY DOES LAME USE INDEPENDENT STEREO as default in higher bitrates ??????Any ideas ? To avoid switching artefacts ? ( Do these switching artefacts interfere more with quality than the gains in bandwidths with JS?)

@greynol - how much data space is a lossless rip for a typical song ? or say 10Mb MPp3 = how many Mb for lossless ? Approx ?

For CDDA lossless compression gets you down to about 60% of the original file size. This is roughly about 850kbps and can vary wildly depending on the source material.

My point is that you only have to do the most tedious and time consuming part once (the ripping) when you archive to a lossless format. Converting to other formats/settings from lossless is relatively effortless.

So, if I got it right, NORMAL is separate left/right encoding and JOINT is modern mid/side joint stereo.

Almost. Read pdq's reply again. Despite what Apple's docs say, joint doesn't mean 100% mid-side, it means each frame can use either mid-side or simple/normal (L-R) stereo, whichever is better. Different encoders have different definitions of "better".

So, an MP3 encoded in joint stereo mode will typically have a mixture of mid-side frames simple stereo frames; the exact ratio varies by encoder, and depends on the characteristics of the music and the encoder's strategy for achieving the desired quality. As the LAME docs point out, switching too often has undesirable effects. One really old encoder was notorious for using 100% mid-side frames.

NOW THIS IS INTERESTING: WHY DOES LAME USE INDEPENDENT STEREO as default in higher bitrates ??????Any ideas ? To avoid switching artefacts ? ( Do these switching artefacts interfere more with quality than the gains in bandwidths with JS?)

It doesn't. That documentation page is years out of date and unreliable. Joint stereo is the default in all encoding modes and has been for years.

So, here is what I currently do: Rip all my CDs with dbpoweramp to AIFF. --- I chose dbpoweramp because to me was much easier to use than EAC, foobar or audiograbber, and instruction was clear. dbpoweramp worked very well so far incl tagging.--- AIFF only because I really wanted to ripriprip, while having some CPU left for typing, email.Than batchconvert to mp3 and ALAC to be used with my iTunes and WMP (apparently there is a way to get this working)

So, here is what I currently do: Rip all my CDs with dbpoweramp to AIFF. --- I chose dbpoweramp because to me was much easier to use than EAC, foobar or audiograbber, and instruction was clear. dbpoweramp worked very well so far incl tagging.--- AIFF only because I really wanted to ripriprip, while having some CPU left for typing, email.Than batchconvert to mp3 and ALAC to be used with my iTunes and WMP (apparently there is a way to get this working)

Thanks to all for answers and help !

UPDATEdbpoweramp works really fine, but unfortunately only for a few rips, after that my whole system freezes/crashes This seems to be a problem of the CD drive/driver of my Thinkpad X301 and unrelated to dbpoweramp as the whole system crashesSupport of dbpoweramp in this problem was excellent, unfortunately there is apparently no solution to this problem.

(no one out there by any chance knowing how to solve this issue???)

Now I am looking into EAC and CueRipper, but apparently none of them reads/rips to AIFF.

AIFF only because I really wanted to ripriprip, while having some CPU left for typing, email.

It would be an old and/or unhealthy computer indeed that could not encode to a lossless format at sensible settings without precluding CPU-negligible tasks such as typing and email. Have you actually tried this and had any problems?